If 'check-gateway' is enabled on an ECMP route, what happens if one of the gateways is unreachable?

When 'check-gateway' is enabled on an Equal-Cost Multi-Path (ECMP) route in MikroTik, the device actively monitors the status of each gateway. If one of the gateways becomes unreachable, it does not continue to send traffic to that gateway. Instead, the routing behavior adjusts accordingly.

The function of excluding the unreachable gateway from future routing decisions ensures that the remaining reachable gateways can still be used for traffic. This operational mechanism enhances fault tolerance and ensures the consistent delivery of packets, as traffic will be distributed among the remaining active gateways without sending packets to an unavailable destination. Thus, this dynamic adjustment to routing tables effectively optimizes the performance and reliability of network traffic in a multi-path routing scenario.